The present invention relates to crushers that use centrifugal force to crush mineral or other such raw materials.
Crushers which employ the centrifugal force generated by a cylindrical rotor rotating at high speed to eject the raw material to be crushed so that it collides with a dead-bed formed around the rotor and is finely crushed are already known.
However, because they employ centrifugal force, crushers of the above-mentioned type have presented the following problems in relation to which improvements have been sought.
1. In order to break the raw material up more finely, one method that is considered is to increase the rotational speed of the rotor and hence the collision speed of the material. However, this requires a larger motor, which increases costs and also generates problems regarding increased weight of the machine.
2. When the rotor rotates at high speed (e.g. above 65 m/sec), the raw material collides at high speed with the surrounding surfaces, producing severe wear and tear of the crusher and leading to problems of durability.
3. To produce crushed material of uniform particle diameter, after crushing, the material is collected up and returned to the crusher to be treated again. However, the amount that must be returned, and the number of times it needs to be returned are so great that productivity is poor.
It is therefore an object of the present invention to provide a crusher which can produce uniform finely pulverised material without having to increase the speed of the rotor, and which has a good rate of productivity.
It is a further object of the present invention to at least go some way to overcoming the disadvantages of the prior art, or at least to provide the public with a useful choice.
In a first aspect the present invention consists in a crusher comprising or including
a cylindrical rotor which rotates about a vertical axis, and a pulverising chamber which houses said rotor, which performs a pulverising process by ejecting raw material to be crushed from ejection ports of rotor so that it collides with a surrounding dead-bed, wherein crushing vanes are provided on an outer face of the rotor protruding radially therefrom, and said crushing vanes are formed with an extension located slightly below a raw material drop point of said dead-bed.
Preferably, the crusher according to the present invention is provided with an annular wall inside said pulverising chamber, and located below the raw material drop point of said dead-bed.
In a second aspect the present invention consists in a crusher as described herein with reference to the accompanying figures.